Fundamental Kotlin is a book focused on Kotlin programming language and it’s comparison to Java. This book is focused on language’s most important features and aspects. Book doesn't go in too much theory since it's focused on exact examples with notes and code provided.
This book is for developers and for people who are on its way to become developers. It is essential to have at least some basic

Kotlin is new programming language running on Java Virtual Machine, Android or browser. It is statically typed language and it can be compiled to JavaScript source code (running on browsers) or native binary as well.